The operation of an aircraft requires the provision of a source of compressed air for pressurizing the cabin of the aircraft and providing other pneumatic services aboard the aircraft. The compressed air used for the pneumatic services has been obtained in different ways. One way is to design the engines of the aircraft in such a way that air can be bleed off from the compressors of the engines and used for the pneumatic services. It is also known to provide auxiliary compressors aboard aircraft and drive them directly or indirectly from the engine. Known direct drive systems utilize an auxiliary shaft which is connected at one end to the engine shaft and at its opposite end to the auxiliary compressor. Known indirect systems utilize a hydraulic pump which is driven by the engine shaft and which in turn drives a hydraulic motor which is connected to the auxiliary compressor.
The efficient operation of advanced technology engines requires the passage of relatively low volumes of compressed air through the engines. Air cannot be bled from these engines for supplying the pneumatic services without severly affecting the function of these engines as the prime mover for the aircraft. If the engines are redesigned so that sufficient engine bleed air is available, the size, weight, and efficiency of the engines is compromised.
Known systems for producing pneumatic services air aboard aircraft, as alternates to bleed air systems, have required compromises in operating efficiencies of the engines over a wide band of operating requirements. The known systems which comprise auxiliary air compressors coupled to the engine either require gear shifting transmissions, or are designed to handle worst case design conditions and operate in surge relief during some of the normal operating conditions. Known systems which comprise remotely powered compressors, driven either by hydraulic motors powered by the hydraulic system aboard the aircraft or electric motors powered by the electric system aboard the aircraft, take substantial amonts of power from the aircraft hydraulic or electrical systems, and are generally also chacterized by costly line losses of power.
The system of the present invention applies recent technological advances in electric motors with the best features of known auxiliary compressor sytems, to produce a maximum efficiency system which does not require the mechanical complexity of gear shifting and/or slip couplings, and which does not experience substantial amounts of power waste.